1. Field of the Invention
The present invention relates to a magneto-optical recording method which allows recording and reproduction of information to be effected simultaneously by means of a laser beam (a light beam), and to a magneto-optical recording medium used in such a method.
2. Related Background Art
A magneto-optical recording medium (hereinafter referred to as a "magneto-optical disc") has recently become of major interest as a recording medium which has a large capacity, which allows rewriting of information, and which is interchangeable.
Information recording on such a magneto-optical disc has been conducted by the following procedures:
(i) An initializing magnetic field is applied to a rotating magneto-optical disc and, at the same time, the portion of the disc where recording is to be effected is irradiated with a laser beam of continuous light so as to erase the previous information; PA1 (ii) Next, a recording magnetic field whose magnetic field orientation is different from that of the initializing magnetic field that is applied to the rotating magneto-optical recording disc and, at the same time, the portion of the disc where recording is to be effected is irradiated with a laser beam modulated in accordance with the recording information so as to effect information recording; and PA1 (iii) Finally, the disc portion where the information recording has been effected is irradiated with a laser beam of a weak continuous light so as to read the recorded information, thereby checking whether the recording has been effected correctly or not. PA1 a first dielectric layer; PA1 a first magnetic layer; PA1 a second magnetic layer which exhibits a higher coercive force at room temperature and a lower Curie temperature as compared with those of the first magnetic layer; PA1 a metal layer of 20 .ANG. or more and 70 .ANG. or less; and PA1 a second dielectric layer, PA1 wherein the metal layer has a heat conductivity which is higher than those of the second magnetic layer and the second dielectric layer.
The checking of (iii) must always be performed since, in magneto-optical recording, it may happen that the recording cannot be correctly performed due to any defect, degeneration and corrosion of the recording medium, dust, any failure of the recording apparatus, etc.
As is apparent from the above description, information recording requires a time corresponding to three rotations of the disc. If it can be performed in a time corresponding to two, or further, one rotation of the disc, the processing speed for the information recording process will be much increased.
To achieve this, various methods have been proposed.
For example, to effect (i) and (ii) simultaneously, (that is, to effect over-write recording), a laser beam of continuous light is applied under an external magnetic field modulated in accordance with recording information.
According to another method, a special medium is used and a laser beam modulated in intensity in accordance with recording information is applied under a D.C. external magnetic field. By adopting such methods, it is possible to perform procedures (i) and (ii) simultaneously and effect information recording in a time corresponding to two rotations of the disc.
Further, in addition to the above methods, there has been proposed a method according to which two laser beams are incorporated into one optical system, and recording is performed by means of the forward beam, and checking of the recording by the rearward beam.
By combining this record checking method with the above-described recording methods, it would be possible to perform procedures (i), (ii) and (iii) simultaneously, effecting information recording in a time corresponding to one rotation of the disc.
However, incorporating two laser beams into one optical system would excessively complicate the optical system. Furthermore, that would require a high level of mechanical precision in the optical system, resulting in an increase in the size of the optical system and in the production costs.